1. Field of the Invention
This invention relates to a 2-stroke cycle internal combustion engine for a vehicle in which a lower amount of blowoff of a gas mixture within a combustion chamber is experienced, fuel consumption is low and exhaust purifying performance is high.
2. Description of Related Art
In the related art 2-stroke cycle internal combustion engine, fuel supplied by a carburetor or the like is mixed with intake air and the gas mixture is sucked into the crank chamber. The gas mixture is supplied into the combustion chamber through the scavenging opening, and a releasing time of the exhaust opening is set faster than a releasing time of the scavenging opening (the upper edge of the opening of the exhaust opening is placed nearer than that of the opening edge of the scavenging opening), resulting in the gas mixture supplied into the combustion chamber being discharged to produce blowoff easily.
Although this blowoff is restricted under an effect of exhaust pulsation movement at the exhaust expansion chamber, its restriction is difficult over the entire operating range, resulting in fuel consumption and influence of the exhaust purifing performance.
In order to solve this problem, there was provided a 2-stroke cycle internal combustion engine disclosed in the official gazette of Japanese Patent Laid-Open No. Hei 5-302521. In the 2-stroke cycle internal combustion engine described in the official gazette of Japanese Patent Laid-Open No. Hei 5-302521, the chamber is arranged near the crankcase and the cylinder block, the intake control valve is placed between the crank chamber and the chamber, the scavenging control valve is placed between the chamber and the combustion chamber, and there is provided a fuel injection valve for use in injecting fuel into the chamber.
In addition, there was provided a 2-stroke cycle internal combustion engine in which an exhaust expansion chamber for restricting blowoff were arranged with an exhaust purifying catalyst device. (See the official gazette of Japanese Utility Model Laid-Open No. Hei 3-127017).
In the 2-stroke cycle internal combustion engine described in the official gazette of Japanese Patent Laid-Open No. Hei 5-302521, all of the intake air in the crank chamber are fed into the chamber through an intake control valve. Furthermore, the air flows into the combustion chamber through the scavenging control valve under a state in which it is mixed with fuel injected from the fuel injection valve into the chamber. Air may not flow from within the crank chamber into the combustion chamber through the scavenging opening, so that blowoff is not be avoided. Although an upstream side port of the scavenging control valve is opened at the lower part of the chamber, it is not the lowest part. Therefore, there is a disadvantage in that fuel injected into the chamber is accumulated at the bottom part of the chamber. As a result, the amount of fuel supplied into the combustion chamber can not be accurately controlled and a response characteristic is poor.
In the 2-stroke cycle internal combustion engine having an exhaust purifying catalyst device disclosed in Japanese Utility Model Laid-Open No. Hei 3-127017, the exhaust expansion chamber has a large capacity, resulting in a motorcycle having an exhaust port arranged at a more forward part of the vehicle body than the combustion chamber. An upstream side opening of the exhaust expansion chamber was connected to the exhaust pipe at the front part of the vehicle body. Furthermore, the exhaust expansion chamber having a larger diameter bypassed below or at a side part of the internal combustion engine and extended to a rearward part of the vehicle body. Thus, an increased minimum ground height and width of the vehicle could not be avoided.